In recent years, in image formation using an inkjet head, high-definition image quality comparable to a photographic image has been demanded. Thus, a droplet amount of an ink discharged from nozzles of the inkjet head is rigorously supervised.
As a conventional example, Patent Document 1 discloses that viscosity of the ink varies due to a change in environmental temperature, a speed of an ink droplet or a volume of the ink droplet varies and, in a driving signal including a first waveform element which expands a capacity of a pressurizing chamber, a second waveform element which holds an expanded state, and a third waveform element which contracts the capacity of the pressurizing chamber to discharge ink droplets, a difference between a potential difference of the first waveform element and the second waveform element and a potential difference of the third waveform element and the second waveform difference is decreased when an environmental temperature is high or increased when the environmental temperature is low.
Patent Document 2 discloses that, when a temperature rises and viscosity of an ink decreases, an amplitude of a driving signal is changed to become small in accordance with a predetermined formula.
Patent Document 3 discloses that a plurality of nozzles of an inkjet head are divided into a plurality of groups each consisting of one or more nozzles, a driving voltage value of expansion pulses is set to become common to the respective groups, and a driving signal which has a driving voltage value of contraction pulses independently set in accordance with the magnitude of a droplet speed for each group is applied to the head, whereby a fluctuation in droplet amount due to a variation of the droplet speed of each nozzle is suppressed.